Prebiotics

The health benefits of consuming dietary fiber have long been established. Both soluble and insoluble fiber play an integral role in maintaining gastrointestinal health, supporting digestion and regular elimination. Research has shown that a high intake of dietary fiber is correlated with lower risks of developing gastrointestinal disorders and several other health conditions, including type 2 diabetes, obesity, coronary artery disease, hypertension, and stroke. (2)

A common misconception is that the terms “fiber” and “prebiotic” are interchangeable. However, while all prebiotics are fibrous carbohydrates, not all fibers can be classified as prebiotics. (42) Compared to the broader classification of dietary fibers, research is only beginning to confirm the unique health effects of prebiotics. (12)

Dietary prebiotics provide fuel for your microbiota, the community of microorganisms residing in your digestive tract.

What are prebiotics?

The current definition describes a prebiotic as “a nondigestible compound that, through its metabolization by microorganisms in the gut, modulates composition and/or activity of the gut microbiota, thus conferring a beneficial physiologic effect on the host”. (12)

Essentially, prebiotics are fibrous carbohydrates that possess unique characteristics and health effects. In order to be classified as a prebiotic, a dietary fiber must:

1. Resist normal digestion and absorption in the gastrointestinal tract
2. Undergo fermentation by intestinal microbiota
3. Confer health benefits to the host through selective stimulation of growth and/or activity of intestinal microbes (38)(42)

While inulin, fructooligosaccharides (FOS), and galactooligosaccharide (GOS) have been well-established as prebiotics, (12) a number of other compounds have also demonstrated prebiotic effects and associated health benefits, such as:

• Arabino-oligosaccharides (12)
• Beta-glucans (12)
• Fructans (26)
• Galactomannan (12)
• Human milk oligosaccharides (5)
• Isomaltooligosaccharide (12)
• Lactulose (12)
• Mannan (45) and glucomannan (17)
• Pectin (13)
• Xylooligosaccharides (12)

Prebiotic vs. probiotic

While prebiotics and probiotics are often described as “synbiotics” since they can work synergistically to support the health of intestinal microbiota, there is a difference between prebiotic and probiotic functions. Prebiotics are non-digestible fibrous carbohydrates fermented by microbes in the digestive tract, essentially acting as “food” and stimulating the growth of beneficial bacteria. Probiotics, on the other hand, are live microorganisms that confer beneficial effects to the host. (31) Probiotics can be obtained from dietary supplements or fermented foods, such as yogurt, cultured vegetables (e.g., kimchi, sauerkraut, pickles), miso, and kombucha. (36)

It’s important to note that, unlike probiotics, prebiotics can only support the growth of bacteria already residing in the gut. (30)

Prebiotic foods include onions, leeks, garlic, asparagus, unripe bananas, mushrooms, and oats.

Prebiotic benefits

Prebiotics are fermented in the gastrointestinal tract, thus acting as a source of fuel for commensal (beneficial) microbes (20), promoting a healthy microbial profile, and providing a number of associated health benefits. (30)

Microbiota

Prebiotics have been shown to promote a favorable composition of intestinal microbiota, particularly by increasing Bifidobacteria and Lactobacilli counts, (12)(30) as well as by decreasing or inhibiting the growth of pathogenic bacteria, such as E. coli, Salmonella spp, and Campylobacter. (12)(42) Improvements in microbial diversity have been shown to support proper immune function and have been associated with a decreased risk of developing allergies. (12)

Metabolites

Furthermore, through their fermentation, prebiotic fibers produce beneficial metabolites. The actions of metabolites, such as short-chain fatty acids (e.g., acetate, propionate, and butyrate), (12)(30) may improve intestinal permeability (12) and immune function. (12)(42) Prebiotics also reduce the fermentation of protein and amino acids and therefore, the subsequent production of potentially harmful metabolites, such as sulfides, ammonia, and amines. (12)(30) Additionally, prebiotics have been shown to improve bioavailability and absorption of certain minerals, such as calcium and magnesium. (12)(42)

The supplementation of various types of prebiotic fibers has also been explored in many health conditions, particularly those related to digestive, cardiometabolic, and immune health, such as:

• Constipation (14)(47)
• Diarrhea, including Traveller’s diarrhea (15) and C.difficile-associated diarrhea (27)
• Irritable bowel syndrome (4)
• Lactose intolerance (40)
• Crohn’s colitis (29)
• Type 2 diabetes (28)(41)
• Obesity and overweight (37)(48)
• Cardiovascular disease (22)(23)
• Hyperlipidemia (10)(46)
• Atopic dermatitis (32)(43)
• Hyperthyroidism (3)
• Polycystic ovary syndrome (PCOS) (16)
• Neonatal hyperbilirubinemia (8)

Sources of prebiotics

Like probiotics, prebiotics may be obtained through the diet or supplementation. The following table provides examples of dietary sources for several compounds that have demonstrated prebiotic effects.

Prebiotics can be obtained by incorporating a variety of the above prebiotic foods into your diet.

Note: Prebiotic supplements and dietary sources have not been associated with any adverse effects when consumed in the correct doses. Flatulence and diarrhea may occur in cases of prebiotic overdose. (31)

The bottom line

Prebiotics are dietary fibers that possess unique characteristics and health effects. Currently, only a small number of fibers have been classified as prebiotics, while many others have demonstrated prebiotic actions. Supplementation with certain prebiotics has also been shown to benefit individuals with a number of digestive, cardiometabolic, immune, and other health conditions.

To learn more about prebiotics and how they may benefit your overall wellness plan, consult an integrative healthcare practitioner who can help you incorporate the most appropriate type and amount of prebiotic fiber into your diet.